Calibrating or Verifying Metal or Steel Tape Measures

T

trainee

#1
Hello everybody!!!
Does anyone has an example of how a tape measure should be calibrated/verified?
I understand the part of verifying that the tape measure is in good condition, with all readings showing and with no broken edges or tips, but I still don't get the part that I need to use a certified steel rule to calibrate it...Why? and how?
Thanks!!!
Thanks!!!!
 
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Jerry Eldred

Forum Moderator
Super Moderator
#2
Re: Calibrating Tape Measures

You use a certified steel rule (precision type, such as sold by Starrett, Mitutoyo, etc.) which is much more accurate than the tape measure.

It is basically the 4:1 uncertainty ratio issue; using a higher accuracy standard. That is why you use the steel rule.

The how depends on what procedure you use. Typically, you check a variety of increments along the length of the tape measure from short to medium to long, check that the end tab accuracy is in spec., check for still visible graticules on the tape measure.

Some tape measure manufacturers are infamous for inconsistent accuracies between graticules because it is painted. That is the biggest issue. Wear and tear of the tape measure, stretching (a more minor issue), and loosening of the end tab (which makes measurements erratically inaccurate).

Essentially you certify a tape measure for the same reasons you certify anything. But as outlined above, those are some of the particulars of issues tape measures have (in my experience).
 
G

Grizz1345

#4
Re: Calibrating Tape Measures

Here:) is my work instruction for checking tape measures. Important that the hook on the end move freely for correct measurement inside and outside.

1 Examine the tape for any external damages or other obvious signs of abuse or wear that may affect the accuracy or function.
2 Clean all surfaces to remove oil and/or any foreign material.
3 Set 40” vernier on a flat counter top or surface plate.
4 Grasp each end of vernier with mic stands to sustain vernier with jaws towards you.
5 Pull tape to desired length. While butting up against inside of vernier jaw, read inside of opposite vernier jaw.
6 Next, while hooking on outside of vernier jaw, read outside of opposite vernier jaw.
7 Always finish reading on the same side of graduates.
8 Document the “as-found” condition on the calibration form.
9 Repeat above 4 steps again at a different length to conclude calibration.

Note:
Accuracy of tapes shall be ± 1/32” (.031”).
Scheduled re-calibration of tapes will require a dimensional report

Hope this all helps.
 
P

Phil Fields

#5
Re: Calibrating Tape Measures

Before you go investing time, money and frustration in calibrating tape measures, what are you measuring, what tolerance are you trying to hold? Is the tape measure graduated in such a way to accurately measure to the tolerance specified? Is the tape measure used more a reference tool?
Phil
 

Frank T.

Involved in Discussions
#6
Re: Calibrating Tape Measures

I had an AS auditor tell me that I don't have to calibrate tape measures or rulers because they are reference measuring instruments and can not be precision measuring instruments. So there was no need to have them calibrated. Is he/she wrong.
 
P

Phil Fields

#7
Re: Calibrating Tape Measures

All of our tape measure are all considered FOR REFERNCE ONLY per our proceudre. This works OK with the auditors.
 
T

trainee

#9
Re: Calibrating Tape Measures

I use them for referece more than anything. My critical characteristics are weight and thickness, and no lenght. But the QA department considers that all measurement instruments must be calibrated...
In my opinion is the characteristic measured is not critical, and the instrument is not used to reference values that will affect the quality of the product, the instrument should not be calibrated...Am I right?
And Thanks everybody for the quick responses!
 
J

John Nabors - 2009

#10
Re: Calibrating Tape Measures

If it doesn't affect product quality, it does not have to be calibrated IMHO.
 
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